The present invention relates generally to the field of magnetic data storage and retrieval systems. In particular, the present invention relates to a thin film transducing head having a bilayer shared pole extension for reduced thermal pole tip protrusion.
In a magnetic data storage and retrieval system, a thin film transducing head typically includes a transducer and a substrate upon which the transducer is built. The transducer, which typically includes a writer portion for storing magnetically-encoded information on a magnetic media and a reader portion for retrieving that magnetically-encoded information from the magnetic media, is formed of multiple layers successively stacked upon the substrate. The volume of the transducer is typically much smaller than the volume of the substrate.
The layers of the transducer, which include both metallic and insulating layers, all have differing mechanical and chemical properties than the substrate. These differences in properties affect several aspects of the transducer. First, the layers of the transducing head will be lapped at different rates. Thus, when an air bearing surface (ABS) of the transducing head is lapped during its fabrication, differing amounts of the layers will be removed—resulting in the transducing head having a uneven ABS. Commonly, a greater amount of the metallic layers of the transducer will be removed during the lapping process than will be removed from the substrate. Thus, this lapping process results in a Pole Tip Recession (PTR) of the metallic layers of the transducer with respect to the substrate. The PTR of a particular layer is defined as the distance between the air bearing surface of the substrate and the air bearing surface of that layer.
The differing mechanical and chemical properties of the substrate and transducer layers further affect the air bearing surface during operation of the transducing head. As the magnetic data storage and retrieval system is operated, the transducing head is subjected to increasing temperatures within the magnetic data storage and retrieval system. In addition, a temperature of the transducing head itself, or a part thereof, may be significantly higher than the temperature within the magnetic data storage and retrieval system due to heat dissipation caused by electrical currents in the transducer.
The coefficient of thermal expansion (CTE) of materials used in forming the substrate is typically much smaller than the CTE of materials used in forming the metallic layers of the transducer. Due to the larger CTE of the transducer's metallic layers, those layers will tend to expand a greater amount than will the substrate. Thus, when the transducing head is subjected to higher operating temperatures, the metallic layers tend to protrude closer to the magnetic disc than the substrate; thereby affecting the PTR of the transducer. This change in PTR caused by temperature is referred to as the Thermal PTR (T-PTR).
During operation of the magnetic data storage and retrieval system, the transducing head is positioned in close proximity to the magnetic media. A distance between the transducer and the media is preferably small enough to allow for writing to and reading from a magnetic medium having a large areal density, and great enough to prevent contact between the magnetic media and the transducer. Performance of the transducer depends primarily on this distance.
The effect of T-PTR on spacing between the transducing head and the magnetic media is more pronounced with metallic layers formed of a high magnetic moment material since such materials tend to have higher CTEs than other metallic materials. A conventional writer includes a shared pole, a top pole, a write via opposite the ABS that extends between the shared and top poles, and a shared pole extension that extends from the shared pole toward the top pole and is separated from the top pole by a write gap. Generally, to increase a strength of a write field produced across the write gap, and thereby promote greater areal densities in the magnetic media, a pole tip portion of the top pole adjacent the ABS and the shared pole extension are formed of a material having a magnetic moment greater than that of the materials forming the remaining metallic layers of the transducing head. However, such high magnetic moment materials tend to have a CTE greater than the more conventional metallic materials used in the transducing head. Thus, given the greater CTE of the high magnetic moment materials needed for the shared pole extension, the potential thermal expansion of the shared pole extension is particularly troublesome.